A liquid crystal display (LCD) is one means for providing an interface between a computer and a computer user. For instance, notebook or laptop computer systems typically have a LCD panel. Most computer LCD panels are illuminated with built-in fluorescent tubes. The tubes may be placed above, beside, or behind the LCD. A cold cathode fluorescent lamp (CCFL) is a common fluorescent tube for providing a uniform white light inside a LCD panel. The LCD often uses a diffusion layer to redirect and scatter the CCFL light evenly. Because the CCFL operates at high AC voltages, the CCFL typically requires a power converter circuit to convert an input DC voltage to an AC voltage.
FIG. 1 depicts a diagram of a backlight LCD system. Inverter 10 receives a DC voltage as input and generates an AC voltage. CCFL 20 is coupled to inverter 10 and uses the AC voltage generated by inverter 10 to generate white light.
The output load of the inverter 10 is set to a level of energy that the inverter 10 must generate in order to adequately power the CCFL 20 to satisfy the system display's brightness setting. The output load may be defined by intensity depending on how much current the CCFL 20 requires for operation. For example, the computer system may operate in a low intensity state when the computer display is set to a non-visible brightness level, a medium intensity state when powered by a battery, and high intensity state when powered by an AC line power outlet. The computer is considered to be in a “battery mode” when the system is powered only by a battery. The computer is considered to be in “AC mode” when the system is powered by an AC line power outlet.
Inverter efficiency is the ratio of the generated inverter output electric power divided by the input electric power. Inverters of a computer system are typically designed to have optimal power conversion efficiency when operated near the maximum output load range. Thus, inverters are often most efficient when the CCFL is in a high intensity light output state.